Skin problems are common both in humans and animals. Often the problems are due to excessive dryness of the skin. Dry skin becomes easily irritated, starts itching and becomes red. When treating sensitive and atopic skin, it is especially important to take care of the moisture balance of the skin. Upon ageing the skin becomes thinner and the maintenance of the moisture balance becomes even more challenging.
Typically, creams and emulsions, applied directly to the skin, are used to treat the excessive dryness of the skin and associated skin problems. Said treatments provide immediate relief. However, this effect does not persist for very long. It is possible to produce a more persistent moisturizing effect by providing special nourishment to the skin. In other words to supply treatment to the skin from inside. Essential fatty acids in the omega-6 and omega-3 groups of fatty acids have a central role.
Dietary strategies for improving skin condition and for prevention and treatment of skin problems as well as use to complement or replace long-term medicinal treatment have been explored. Dietary formulations based on natural oils extracted from seeds of sunflower, flax (or linseed), black currant, evening primrose, borage (or starflower), echium, hemp and sea buckthorn oil as well as fish oils, have been used as nutritional aids in the skin health area.
Fatty acids such as linoleic acid (LA), alpha-linolenic acid (ALA), gamma-linolenic acid (GLA), stearidonic acid (SDA), palmitoleic acid (POA), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are components of these oils and have been identified as being important fatty acids with biological activity regarding skin health.
Linoleic acid (LA) and alpha-linolenic acid (ALA) are considered to be essential fatty acids for humans and animals, because they are not synthesized in the body and therefore are required to be obtained through the diet. Gamma-linolenic acid (GLA) and stearidonic acid (SDA) are the immediate metabolites of LA and ALA, respectively (FIG. 1).
In popular media and commercial messages involving dietary fatty acid supplements the ratio of dietary omega-6 and omega-3 groups of fatty acids of 5:1 is considered to be optimal to support various aspects of human health. Expert committees have concluded that the use of omega-6 and omega-3 ratio of 5:1 or any other ratio as guidance for nutritional adequacy is not helpful and may in fact distort the analysis of dietary fatty acid intake data [de Deckere et al. 1998]. Use of simpler ratio of LA to ALA has been recommended until more is known about the relative potencies of various n−3 fatty acid types [Anonymous 1992].
Because the enzyme that produces GLA from LA, Δ-6 desaturase, has low activity in the skin, dietary GLA is thought to be important for skin health [Ziboh and Chapkin 1987]. Combinations of dietary GLA and EPA are thought to be more effective than GLA alone with respect to skin health [Miller et al. 1991]. Thus, number of fatty acids with bioactivity towards the skin has been identified, but no consensus with respect to optimal fatty acid ratios exists.
Nutritional treatment of skin problems is the object of growing interest because of the benefits it can offer to subjects in need of said treatment. However, there are problems associated with the current lipid compositions and methods for treating skin problems.
Callaway et al. (2005) report on a clinical trial where hempseed oil was shown to be effective in alleviating some of the symptoms of atopic dermatitis at a dose of 30 mL/day. It is not clear whether the improvement in the skin condition was due to improved skin barrier function, because there was only a non-significant reduction in transepidermal water loss. The problem with the hemp seed oil supplementation is that the effective daily dose of 30 ml is fairly large and this may become a problem for some individuals not being able to ingest large amounts of oil on a daily basis.
Borage oil is a rich source of GLA and therefore it is often used alone or in combination with other natural oils in nutritional oil compositions for skin health. However, its applicability as a single oil product for skin health may be limited by its fatty acid profile consisting of high levels of omega-6 fatty acids, LA and GLA.
Natural oils are typically blended for use in nutritional oil compositions since no single fatty acid has been shown to be effective. Typically, GLA containing oils are blended with fish oil to create a mixture of omega-6 and omega-3 fatty acids that controls the inflammatory process in the skin [Ziboh et al. 2000]. The problem with fish oil containing compositions is that many people choose not to use them because of fish allergies or sensitivity to fish taste associated with the intake of fish oil containing lipid formulations (so called fishy burps).
Sea-buckthorn oil is rich in palmitoleic acid (C16:1 or POA). There is convincing evidence that sea-buckthorn oil improves the condition of mucous membranes, but the evidence that the oil or its component fatty acid, POA, has efficacy on the epidermis of the skin is less consistent [Yang and Kallio 2002].
As presented in WO 2010/067206, a composition specifically directed for use in nutrition of companion animals, has been shown to alleviate skin problems of an animal when added to the food of the companion animal. An advantage of the said lipid composition for the companion animals is the fixed ratios of the essential fatty acids (linoleic acid, LA and alpha-linolenic acid, ALA) as well as their immediate metabolites (gamma-linolenic acid GLA and stearidonic acid SDA). The disadvantage of this lipid composition for use in human subjects is the large effective dose of 20 ml/d.
There is an evident need for a low dose, well-tolerated and efficient lipid composition for treatment of skin problems.